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First Report of Fusarium Ear Rot of Maize Caused by Fusarium andiyazi in China

Maize (Zea mays L.) is an important food crop worldwide. Some Fusarium species cause maize ear rot leading to significant yield losses and, for some Fusarium species, potential risk of mycotoxin contamination. In 2013, a survey was conducted to determine the population composition of Fusarium species on maize in Dongyang, Zhejiang Province, China, where about 5% of maize ears in each field were found with reddish-white mold. Symptomatic maize ears were collected from several cultivars including forage corn Zhedan724 and Zhengdan958, sweet corn Chaotian4 and Chaotian135, and waxy corn Heinuo181 and Zhenuoyu6; no association between the disease and maize cultivars was observed. Maize kernels showing a pink or white mold were surface-disinfested with 70% ethanol and 10% sodium hypochlorite, followed by three rinses with sterile distilled water and placed onto potato dextrose agar (PDA). After 3 days of incubation at 25°C in the dark, mycelia were transferred to fresh PDA and purified by the single-spore isolation method (4). Species were identified based on morphological characteristics (2), and sequence analysis of the translation elongation factor-1α (TEF) gene. The results indicated that Fusarium verticillioides Sacc. (84.6%) is the main causal agent of maize ear rot in this region. However, morphological characteristics of two strains (7.7%) from the same field were found to be identical to F. andiyazi Marasas, Rheeder, Lampr., K.A. Zeller & J.F. Leslie. Colonies on PDA showed floccose to powdery mycelium and pale-purple pigmentation. Hyaline and straight or slightly curved macroconidia were observed with 3- to 6-septate and a slightly curved apical cell. Chlamydospores were absent. In order to validate this result, partial translation elongation factor (TEF-1α, 646 bp) gene sequences of isolates were generated (GenBank Accession No. KJ137019) (1). BLASTn analysis of TEF-1α with the GenBank database revealed 99.7% sequence identity to F. andiyazi (JN408195 and JN408196), and much lower (94 to 98%) identity with other Fusarium spp. Thus, both morphological and molecular criteria supported identification of the strains as F. andiyazi. A pathogenicity test was performed on maize cv. Zhengdan958 in a greenhouse. Four days post-silk emergence, a 2-ml conidial suspension (10⁵ macroconidia/ml) of each isolate was injected into each of 10 maize ears through the silk channel. An equal amount of sterile distilled water was injected into 10 ears as a control. Typical Fusarium ear rot symptoms (reddish-white mold), which were observed in the ears inoculated with these strains 20 days after inoculation, were similar to the original symptoms in the sampling sites, and no symptoms were observed on the water control ears. The same fungus was re-isolated from the infected kernels using the method described above. F. andiyazi are the major pathogens of sorghum (2) and also proved to attack maize kernels recently (3). To our knowledge, this is the first report of F. andiyazi causing Fusarium ear rot on maize in China. Further investigation is needed to gain a better understanding of the spatial and temporal dynamics of this new pathogen. Also, the new species must be considered in the development of maize cultivars with broad-based resistance to the pathogens.

References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Ames, IA, 2006. (3) A. Madania et al. J. Phytopathol. 161:452, 2013. (4) H. Zhang et al. PLoS ONE 7:e31722, 2012.